Ecosystems Go to the Birds

The alarming trend of avian extinctions may be more than just a tragedy for bird lovers; they could have dire consequences for the ecosystems on which all life depends, a new study indicates.

Birds are among the best studied organisms on the planet. So when Cağan Sekercioğlu, a conservation ecologist at Stanford University in California, went looking for a simple statistic--the percentage of insectivorous birds that are threatened worldwide--he was surprised to find it didn't exist. That spurred him and colleagues to painstakingly gather data on the world's 9787 known living and 129 extinct bird species. They compiled information on each species' conservation status, distribution, life history, ecological role, and threats.

The team then assessed the proportion of extinction-prone species among major ecological and geographical groupings. Overall, 21% of bird species are extinction-prone and 6.5% are functionally extinct (that is, either extinct or there are so few that they matter little to ecosystems anymore). Projecting to 2100, the team calculated the percentage of extinction-prone species under three scenarios. Even in the best case, in which conservation measures prevent further species from becoming threatened, they predicted that 700 species will be functionally extinct by 2100. In the worst case, some 25% could be lost.

Most at risk would be scavengers, herbivores, fish-eaters, fruit-eaters, and nectar-feeders, as would those with very specialized diets or habitat requirements. The habitats likely to lose the most bird species are forests, seas, and wetlands, while island regions such as Madagascar, New Zealand, and Oceania would lose the greatest percentage, the researchers report online in the Proceedings of the National Academy of Sciences.

Because birds play important roles as pollinators, seed dispersers, fertilizers, carrion-eaters, and in keeping down insect pests, these extinctions could have profound consequences for natural ecosystems, agriculture, and human health, the researchers say. For instance, the crash of vulture populations in the Indian subcontinent (ScienceNOW, 1 October ) has been linked to a boom of scavenging dogs that carry rabies.

The uneven spread of extinction-prone species across ecological and geographical groupings will likely mean "even greater ecological consequences and ecosystem dysfunction than global figures suggest," says Stuart Butchart, coordinator of BirdLife International's Global Species Programme in Cambridge, United Kingdom.